1. Field of the Invention
The present invention relates to an apparatus and a method to correct a reference voltage, more especially to an apparatus and a method to correct a reference voltage to enable the reference voltage of electric devices to be corrected using software.
2. Description of the Related Art
Each of electric devices included in a digital system exchange data via a bus. The data exchanged via the bus has a digital form represented as an electrical 1 (high) or 0 (low). The electric devices recognize the data by recognizing a combination of 0 and 1 in transferred digital signals.
Accordingly, the electric devices have a reference voltage (Vref) to discriminate whether a received signal is 0 or 1. That is, if a voltage of the received signal is higher than the Vref, then the electric devices recognize the received signal as 1, or else if the voltage for the received signal is lower than the Vref, then the electrical devices recognize the received signal as 0.
FIG. 3 is a schematic view illustrating a circuit of a conventional device supplying the reference voltage Vref. Specifically FIG. 3 illustrates the circuit to supply the reference voltage Vref to two electric devices exchanging the digital data via the bus connected between each other.
As shown in FIG. 3, digital devices A and B 101 and 103 are provided to input/output the digital data between each other via a bus 105. The digital data is in a form of a signal electrically discriminated as 1 or 0, and, thus, the digital device A 101 and B 103 receive the Vref in order to discriminate the received signal.
The Vref is generally laid out so as to be output from a node between two resistors R1120 and R2106 connected in series to a VDD line, which is a main supply voltage of digital devices. The R1120 and the R2106 are fixed resistors and, thus, once laid out, it is impossible to adjust a resistance of the resistors R1120 and R2106.
Recently, as an operating speed of the electric devices is gradually increasing, noise in the digital data signal frequently occurs. Accordingly, accuracy of the Vref has been emphasized for accurate recognition of the digital data signal.
Also, in a case of transforming characteristics of the digital data signal with respect to (electromagnetic interference) EMI and, thus, tuning data transfer efficiency, the Vref is also to be adjusted according to the transformed data signal. In a case of adjusting the Vref, a user cannot manually connect resistors having different resistance values to a circuit in order to find appropriate new resistors R1 and R2 corresponding to an intended Vref, and if the user finds the appropriate new resistors R1 and R2, then the user has to change the old R1 and R2 to the new ones having an appropriate resistance value manually.